Process For Recovering Solvent From Ashphaltene Containing Tailings Resulting From A Separation Process

ABSTRACT

A process for recovering paraffinic solvent from tailings produced in the treatment of bitumen froth comprising introducing the tailings into a tailings solvent recovery unit (TSRU), the TSRU having internals, and distributing the tailings over the internals. An inert gas or steam is then introduced below the internals and above the liquid pool for enhancing the vaporization of the contained solvent. Solvent is vaporized from asphaltene agglomerates. In one embodiment, the process is affected in the absence of mechanical means used to substantially break up asphaltene agglomerates or to prevent the agglomeration of asphaltene. In another aspect, the process comprises introducing the tailings into a first TSRU as described above and then into a second TSRU operated at a lower pressure. In another aspect, internals are optionally present and steam or inert gas is injected in the liquid pool.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Canadian patent applicationnumber 2,587,166 which was filed on May 3, 2007.

FIELD OF THE INVENTION

The present invention relates generally to an improved process forrecovering solvent from asphaltene containing tailings resulting from aseparation process. More particularly, the invention relates torecovering paraffinic solvent from such tailings.

BACKGROUND OF THE INVENTION

The extraction of bitumen from mined oil sands involves the liberationand separation of bitumen from the associated sands in a form that issuitable for further processing to produce a marketable product. Amongseveral processes for bitumen extraction, the Clark Hot Water Extraction(CHWE) process represents a well-developed commercial recoverytechnique. In the CHWE process, mined oil sands are mixed with hot waterto create slurry suitable for extraction. Caustic is added to adjust theslurry pH to a desired level and thereby enhance the efficiency of theseparation of bitumen. Recent industry developments have shown thefeasibility of operating at lower temperatures and without causticaddition in the slurrying process.

Regardless of the type of water based oil sand extraction processemployed, the extraction process will typically result in the productionof a bitumen froth product stream comprising bitumen, water and finesolids (also referred to as mineral matter) and a tailings streamconsisting of essentially coarse solids and some fine solids and water.A typical composition of bitumen froth is about 60 wt % bitumen, 30 wt %water and 10 wt % solids, with some variations to account for theextraction processing conditions. The water and solids in the froth areconsidered as contaminants and must be either essentially eliminated orreduced to a level suitable for feed to an oil refinery or an upgradingfacility, respectively. The contaminants rejection process is known as afroth treatment process and is achieved by diluting the bitumen frothwith a sufficient quantity of an organic solvent such as naphtha. Thereare two commercial approaches to reject the froth contaminants, namelynaphtha based and paraffinic solvent based. Solvent addition (dilution)increases the density differential between bitumen and water and solidsand as well enable the contaminants rejection using multi-stage gravitysettling units. The separation schemes generally result in a bitumendiluted product and another tailings stream, commonly referred to as thefroth treatment tailings, containing residual bitumen, residual solvent,solids and water. The froth treatment tailings stream must be processedfurther to recover the residual solvent and be suitable for disposal.Residual solvent recovery is dictated by both environmental and economicreasons. This recovery operation is referred to as a tailings solventrecovery process.

In the naphtha based separation, the resulting bitumen product contains1 to 3 wt % water and <1.0 wt % solids and is not suitable fortransporting through a common pipeline carrier. The addition ofsufficient amounts of paraffinic solvent results in asphalteneprecipitation, formation of aggregates with the contaminants (entrainedwater and carryover solids in the froth) and a rapid settling to providea solids free dry bitumen product suitable for transportation in acommon carrier and to refineries.

The addition of paraffinic solvent to bitumen froth and the resultingbenefits are described in Canadian Patents Nos. 2,149,737 and 2,217,300.According to Canadian Patent No. 2,149,737, the efficiency (rate andextent) of removal of water and solids generally increases as (i) thecarbon number or molecular weight of the paraffinic solvent decreases,(ii) the solvent to froth ratio increases, and (iii) the amount ofaromatic and naphthene impurities in the paraffinic solvent decreases.The inventors further demonstrated that the separation of water andsolids from the bitumen is achieved at temperatures above 30° C. Theeffect of temperature on bitumen recovery and bitumen product qualityobtainable in this separation process was studied in a scale up pilotusing natural gas condensate (NGC) which contains about 83% paraffin.While bitumen recovery was higher (97.6 vs. 83.8 wt %) if the run wasconducted at 117° C., the product quality obtained was significantlylower (99.2 vs. 90.6 wt %) than obtained at 50° C. In accordance withthe one of the discoveries stated above, the inventors used a relativelyhigh solvent/froth ratio to obtain a better product quality with NGC ina continuous process but this test was done at 50° C. Although theinventors obtained a satisfactory product quality using pure paraffinicsolvents at laboratory conditions and up to 80° C., it was not obvioussuch a result would be duplicated at a pilot scale continuous test unitdue to uncertain hydrodynamics as well as increasing solubility of waterin hydrocarbon at higher temperatures. In general, in a continuousseparation, product quality and yield are inter-related and judiciousfine-tuning of process parameters is required to establish optimumquality for a given yield. As discussed above, the froth treatmentprocess must have a reliable and economic technique for solvent recoveryfrom the tailings. However, the unique nature of the solvent-containingtailings makes solvent removal a challenge to the industry. Variousprocesses have been devised for recovering solvent fromsolvent-containing tailings, some of which will now be described.

Canadian Patent No. 1,027,501 describes a process for treatment oftailings to recover naphtha. The process comprises introducing thetailings into a distributor at the upper end of the chamber of a vacuumflash vessel or tower maintained at 35 kPa, in order to flash thenaphtha present in the tailings. The vessel is also equipped with astack of internal shed decks for enhancing contact between strippingsteam and the tailings feed. The steam is introduced at a point abovethe liquid pool in the vessel and below the stack of shed decks. Thesteam is intended to heat the flashed tailings as they pass down throughthe shed decks, to vaporize contained solvent and some water, forrecovery as an overhead stream. In practice, however, this processresults in only 60 to 65% recovery of the solvent; hence, a large amountof solvent is still being released to the environment.

Canadian Patent No. 2,272,045 describes a method for recovery ofhydrocarbon solvent from tailings produced in a bitumen froth treatmentplant comprising introducing the tailings into a steam stripping vesselmaintained at near atmospheric pressure, the vessel having a pluralityof interior, vertically spaced shed decks, and distributing the tailingsover said shed decks. Steam is introduced below the shed decks forvaporizing the major portion of the contained solvent and some water.However, the tailings are free of asphaltenes according to page 4, lines11 to 13. Canadian Patent No. 2,272,035 describes a process for recoveryof hydrocarbon solvent from tailings produced in a bitumen frothtreatment plant comprising introducing the tailings into a vacuum flashvessel maintained at a sufficiently low sub-atmospheric pressure tovaporize the major portion of the contained solvent and some water. Theresiduals then pool near the bottom of the flash vessel. Steam is thenintroduced into the tailings pool for vaporizing residual solvent andsome water. However, as with Canadian Patent No. 2,272,045, discussedabove, the tailings are free of asphaltenes according to page 4, lines12 to 15. Thus, the inventors of these two patents did not have tocontend with the challenges associated with having asphaltenes in thetailings. Certain of such challenges are discussed below with referenceto Canadian Patent No. 2,353,109 and Canadian Patent Application No.2,454,942.

Canadian Patent No. 2,353,109 describes a process for treating anunderflow stream (or tailings) containing water, solvent, asphaltenesand solids, from one of the last separation steps in a paraffinicsolvent process for separating bitumen from an oil sands froth, whereina) the stream is introduced to a solvent recovery vessel that issubstantially free of internals wherein the temperature and pressure aresuch that the solvent is normally a vapor; b) a pool of liquid andsolids is maintained in the lower part of the vessel at a controlledlevel for sufficient time to allow the solvent to vaporize; c) the poolis agitated to the point where the asphaltenes are dispersed, submergedand prevented from re-agglomerating and the solids are maintained insuspension; d) the solvent is recovered as an overhead vapor stream; ande) the solvent depleted remainder of the stream is removed from thebottom of the vessel as a liquid slurry. Agitation is preferablyeffected by means of an impeller. An alternate agitation means is apump-around circuit to pump the slurry from the top of the liquid poolto the lower part of the liquid pool or vice versa. The typicalcomposition of this underflow stream is described as about 40 to 60 wt %water, about 15 to 35 wt % mineral solids (sand and clay), about 5 to 15wt % entrained solvent, and about 10 to 15 wt % asphaltenes andunrecovered bitumen. Page 3, second full paragraph of that patentdescribes (a) that conventional solvent technology employs vessels withinternals such as trays, packing and baffles; (b) that such internalsprovide the residence time required for the necessary solventvaporization to take place; (c) that vessels with such internals are notpractical for an underflow stream having the aforementioned composition;(d) that the aforementioned conventional approach is unworkable becauseof the accumulation of inorganic and organic solids and the fouling orplugging of vessel internals, lines and valves; and (e) that in thatinvention, the necessary residence time is achieved by having a liquidpool form in the lower part of the vessel. The invention teaches thatagitation must be provided in or around the solvent recovery unitprimarily to disperse or prevent the growth of aggregates ofprecipitated asphaltenes thereby enhancing the release of solvent fromthe precipitated asphaltenes to the vapor phase. In one embodiment,first and second stage solvent recovery vessels are used, where thesecond stage vessel is typically operated at a reduced pressure relativeto the first stage vessel to reduce any amount of foam that may still beassociated with the liquid slurry removed from the bottom of the firststage vessel. The second stage vessel is mechanically identical to thefirst stage vessel.

Canadian Patent Application No. 2,454,942 describes a process forsolvent recovery from froth treatment tailings comprising water,particulate solids, and precipitated asphaltenes. According to theinventors, recycling a pre-determined portion of the solvent recoveredtailings stream to the solvent recovery apparatus is necessary tomaintain downward flux in the apparatus which inhibits accumulation ofasphaltene mat in the solvent recovery unit and suppress the formationof foam. Furthermore, shearing conditions (provided by pumps, mixers oranother apparatus) is preferably provided in the recycle circuit first,to break up asphaltene flocs/aggregates and second, to enhance recoveryof solvent from the tailings. There is no introduction of steam or inertgas to vaporize solvent from the asphaltenes.

Thus, Canadian Patents Nos. 2,272,045 and 2,272,035 deal with solventrecovery from tailings that are free of asphaltenes. Canadian Patent No.2,353,109 deals with solvent recovery without the use of internals.Canadian Patent Application No. 2,454,942 deals with solvent recoverywithout the introduction of steam or inert gas to vaporize solvent fromthe asphaltenes. Both of Canadian Patent No. 2,353,109 and CanadianPatent Application No. 2,454,942 deal with solvent recovery fromtailings containing asphaltenes using agitation or shearing in or aroundthe recovery vessel, so that the asphaltenes are dispersed, submergedand prevented from re-agglomerating.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at leastone disadvantage of previous processes.

In a first aspect, the present invention provides a process forrecovering paraffinic solvent from froth treatment tailings produced inthe treatment of bitumen froth comprising: introducing the frothtreatment tailings into a tailings solvent recovery unit (TSRU), theTSRU having internals, and distributing the froth treatment tailingsover the internals to increase the surface area of the froth treatmenttailings; introducing inert gas or steam below the internals so that itflows counter currently to the froth treatment tailings and heats thefroth treatment tailings to vaporize at least a portion of theparaffinic solvent; and removing the vaporized solvent from the TSRU;wherein the froth treatment tailings contain asphaltenes; and whereinthe at least a portion of the solvent is vaporized from asphalteneagglomerates.

Within this first aspect, the following embodiments may be included. Theprocess may be affected in the absence of mechanical means used tosubstantially break up asphaltene agglomerates or to prevent theagglomeration of asphaltene. The TSRU may have an absolute pressure ofabout 100 and about 200 kPa. The internals may comprise a plurality ofinterior, vertically spaced shed decks. The internals may be coated withan asphaltene fouling resistant coating to mitigate fouling or pluggingin the TSRU. The froth treatment tailings may contain at least 1.0 wt %asphaltenes, or at least 5.0 wt % asphaltenes. The inert gas or steamintroduced below the internals may be introduced above a liquid levelthat forms in the bottom of the TSRU. The paraffinic solvent may be a C₄to C₆ paraffinic hydrocarbon solvent. The paraffinic solvent may bepentane, iso-pentane, or a combination thereof. The temperature of theTSRU may be about 75 to about 100° C. The TSRU may have an absolutepressure of about 120 to about 170 kPa. The inert gas may be nitrogen,methane, carbon dioxide, argon, steam or any other inert gas that is notreactive under process conditions. The inert gas or steam to frothtreatment tailings mass ratio may be about 1:1 to about 10:1. Theprocess may further comprise: feeding tailings from the TSRU into asecond TSRU maintained at an absolute pressure that is lower than thepressure of the TSRU recited above, the second TSRU having internals,and distributing the tailings from the TSRU over the internals toincrease the surface area of the tailings from the TSRU; introducinginert gas or steam below the internals of the second TSRU so that itflows counter currently to the tailings from the TSRU and heats thetailings from the TSRU to vaporize at least a portion of the paraffinicsolvent; and removing the vaporized solvent from the second TSRU. Thesecond TSRU may have an absolute pressure of about 20 to about 200 kPa.The internals of the second TSRU may comprise a plurality of interior,vertically spaced shed decks. The inert gas or steam introduced belowthe internals in the second TSRU may be introduced above a liquid levelthat forms in the bottom of the second TSRU. The second TSRU may have anabsolute pressure of about 35 kPa to about 125 kPa, or about 35 kPa toabout 100 kPa. The temperature of the second TSRU may be about 75 toabout 100° C.

In a second aspect, the present invention provides a process forrecovering paraffinic solvent from froth treatment tailings produced inthe treatment of bitumen froth comprising: introducing the frothtreatment tailings into a first tailings solvent recovery unit (TSRU),the first TSRU having internals; distributing the froth treatmenttailings over the internals to increase the surface area of the frothtreatment tailings; introducing inert gas or steam below the internalsso that it flows counter currently to the froth treatment tailings andheats the froth treatment tailings to vaporize at least a portion of theparaffinic solvent; removing the vaporized solvent from the first TSRU;feeding tailings from the first TSRU into a second TSRU maintained at anabsolute pressure that is lower than the pressure of the first TSRU, thesecond TSRU having internals; distributing the tailings from the firstTSRU over the internals of the second TSRU to increase the surface areaof the tailings from the first TSRU; introducing inert gas or steambelow the internals of the second TSRU so that it flows countercurrently to the tailings from the first TSRU and heats the tailingsfrom the first TSRU to vaporize at least a portion of the paraffinicsolvent; and removing the vaporized solvent from the second TSRU.

Within this second aspect, the following embodiments may be included.The TSRU may have an absolute pressure of about 100 and 200 kPa and thesecond TSRU may have an absolute pressure of 20 to 200 kPa. Theinternals may comprise interior, vertically spaced shed decks. Theinsert gas or steam introduced below the internals may be introducedabove a liquid level in the first and second TSRU's. The froth treatmenttailings may contain asphaltenes, at least a portion of the solvent maybe vaporized from asphaltene agglomerates, and the process may beaffected in the absence of mechanical means used to substantially breakup asphaltene agglomerates or to prevent the agglomeration ofasphaltene. The froth treatment tailings may contain at least 1.0 wt %asphaltenes, or at least 5.0 wt % asphaltenes. The paraffinic solventmay be a C₄ to C₆ paraffinic hydrocarbon solvent. The paraffinic solventmay be pentane, iso-pentane, or a combination thereof.

In a third aspect, the present invention provides a process forrecovering paraffinic solvent from froth treatment tailings produced inthe treatment of bitumen froth comprising: introducing the frothtreatment tailings into a tailings solvent recovery unit (TSRU);introducing inert gas or steam into a liquid pool formed in the bottomof the TSRU to vaporize at least a portion of the paraffinic solvent;and removing the vaporized solvent from the TSRU; wherein the frothtreatment tailings contain asphaltenes; and wherein the at least aportion of the solvent is vaporized from asphaltene agglomerates.

Within this third aspect, the following embodiments may be included. TheTSRU may be substantially free of internals. The process may be affectedin the absence of mechanical means used to substantially break upasphaltene agglomerates or to prevent the agglomeration of asphaltene.The froth treatment tailings may contain at least 1.0 wt % asphaltenes,or at least 5.0 wt % asphaltenes. The TSRU may have an absolute pressureof about 20 and about 200 kPa. The paraffinic solvent may be a C₄ to C₆paraffinic hydrocarbon solvent. The paraffinic solvent may be pentane,iso-pentane, or a combination thereof. The temperature of the TSRU maybe about 75 to about 100° C. The process may further comprise feedingtailings from the TSRU into a second TSRU maintained at an absolutepressure that is lower than the pressure of the TSRU recited above.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figure, wherein:

FIG. 1 is a schematic of a diluted bitumen froth treatment process,including a tailings solvent recovery process according to an embodimentof the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Generally, the present invention provides, in one aspect, a process forrecovering paraffinic solvent from tailings produced in the treatment ofbitumen froth comprising introducing the tailings into a tailingssolvent recovery unit (TSRU), the TSRU having internals, anddistributing the tailings over the internals. An inert gas or steam isthen introduced below the internals for enhancing the vaporization ofthe contained solvent. Solvent is vaporized from asphalteneagglomerates. In one embodiment, the process is affected in the absenceof mechanical means used to substantially break up asphalteneagglomerates or to prevent the agglomeration of asphaltene. In anotheraspect, the process comprises introducing the tailings into a first TSRUas described above and then into a second TSRU operated at a lowerpressure.

It has been shown that prior art methods of agitation or use of shearingdevices in the recovery of solvent from diluted tailings containingasphaltene agglomerates actually results in significant increase inoperability problems such as plugging and fouling as well as lowersolvent recovery.

FIG. 1 is a schematic of a diluted bitumen froth treatment process,including a tailings solvent recovery process according to an embodimentof the present invention. The paraffinic solvent diluted bitumen froth(2) enters froth separation unit FSU (4).

The diluted bitumen froth (2) may be produced in a number of ways knownin the art and comprises bitumen, asphaltenes, mineral solids, water,and a paraffinic solvent.

The diluted bitumen froth (2) contains a paraffinic solvent because sucha solvent has been added to a bitumen froth to induce precipitation of aportion of the asphaltenes present in bitumen, aggregation with waterdroplets and solids present in froth and settling rapidly in a gravitysettler (FSU).

The term “paraffinic solvent” (also known as aliphatic) as used hereinmeans solvents containing normal paraffins, isoparaffins and blendsthereof in amounts greater than 50 wt %. Presence of other componentssuch as olefins, aromatics or naphthenes counteract the function of theparaffinic solvent and hence should not be present more than 1 to 20 wt% combined and preferably, no more than 3 wt % is present. Theparaffinic solvent may be a C₄ to C₂₀ paraffinic hydrocarbon solvent orany combination of iso and normal components thereof. In one embodiment,the paraffinic solvent comprises pentane, iso-pentane, or a combinationthereof. In one embodiment, the paraffinic solvent comprises about 60 wt% pentane and about 40 wt % iso-pentane, with none or less than 20 wt %of the counteracting components referred above.

By using a blend of pure paraffins and operating at a temperature rangeof 70 to 90° C. in a continuous separation unit as shown in FIG. 1, itis possible to achieve both a high quality (containing <0.01 wt %, or atleast <0.5 wt. %, water+solids) and a high yield (98 wt %) bitumenproduct.

With the addition of a sufficient amount of paraffinic solvent, and byway of gravity settling, the diluted bitumen froth (2) separates in FSU(4) into a diluted bitumen component (6) comprising bitumen and solventand a froth treatment tailings component (8) comprising mainly of water,mineral matter, precipitated asphaltenes, solvent, and very smallamounts of unrecovered bitumen. The tailings stream (8) may be withdrawnfrom the bottom of FSU (4), which may be conical. In one embodiment, FSU(4) operates at a temperature of about 60° C. to about 80° C., or about70° C. In one embodiment, FSU (4) operates at a pressure of about 700 toabout 900 kPa, or about 800 kPa.

Diluted bitumen component (6) is passed through a solvent recovery unit,SRU (10), such as a conventional fractionation vessel or other suitableapparatus in which the solvent (12) is flashed off and condensed in acondenser associated with the solvent flashing apparatus andrecycled/reused in the process. The solvent free bitumen product (14) isthen stored or transported for further processing in a manner well knownin the art.

Froth treatment tailings component (8) may be passed directly to thetailings solvent recovery unit, TSRU, (16) or may, as shown in FIG. 1,first be passed to a second FSU (18). Diluted tailings component (8) maytypically comprise approximately 50 to 70 wt % water, 15 to 25 wt %mineral solids, and 5 to 25 wt % hydrocarbons. The hydrocarbons compriseasphaltenes (for example 2.0 to 12 wt % or 9 wt % of the tailings),bitumen (for example about 7.0 wt % of the tailings), and solvent (forexample about 8.0 wt % of the tailings). In further embodiments, thetailings comprise greater than 1.0, greater than 2.0, greater than 3.0,greater than 4.0, greater than 5.0, or greater than 10.0 wt %asphaltenes.

Tailings component (8) is a tailings stream generated in aparaffinic-based bitumen froth treatment process or other separationprocess and while certain means resulting in a froth treatment tailingscomponent have been described above, the present invention is notlimited thereby.

FSU (18) performs generally the same function as FSU (4). The operatingtemperature of FSU (18) may be higher than that of FSU (4) and may bebetween about 80° C. and about 100° C., or about 90° C. In oneembodiment, FSU (18) operates at a pressure of about 700 to about 900kPa, or about 800 kPa. A diluted bitumen component stream (20)comprising bitumen and solvent is removed from FSU (18) and is eithersent to FSU (4) feed for use as solvent to induce asphaltene separationor is passed to SRU (10), or to another SRU, for treatment in the sameway as the diluted bitumen component (6). The ratio of solvent:bitumenin diluted bitumen component (20) may be, for instance, 1.4 to 30:1, orabout 20:1 in the configuration shown in FIG. 1. Alternatively, dilutedbitumen component (20) may be partially passed to FSU (4) and partiallypassed to SRU (10), or to another SRU. Solvent (12) from SRU 10 may becombined with the diluted tailing stream (8) into FSU (18), shown asstream (22), or returned to a solvent storage tank (not shown) fromwhere it is recycled to make the diluted bitumen froth stream (2), thus,streams (20) and (22) show recycling. In the art, solvent or dilutedfroth recycling steps are known such as described in Canadian Patent No.2,021,185.

The froth treatment tailings (8) or tailings component (24) (with acomposition similar to underflow stream (8) but having less bitumen andsolvent), is combined with dilution water (25) to form diluted tailingscomponent (26) and is sent to TSRU (16). The dilution water may be atabout 70° C. to about 95° C., or about 90° C. and the addition rate mayvary between 0.5 to 2.0 times the mass of the tailings stream (8) or(24). Diluted tailings component (26) may be pumped from the FSU (18) orFSU (4) (for a single stage FSU configuration) to TSRU (16) at the sametemperature and pressure in FSU (18) or FSU (4), as the case may be. Abackpressure control valve may be used before an inlet into TSRU (16) toprevent solvent flashing prematurely in the transfer line between FSU(18) and TSRU (16). The operation of TSRU (16) is discussed in moredetail below.

Flashed solvent vapor and steam (together 27) is sent from TSRU (16) toa condenser (28) for condensing both water (30) and solvent (32).Recovered solvent (3) may be reused in bitumen froth treatment. Tailingscomponent (34) may be sent directly from TSRU (16) to a tailings storagearea for future reclamation or, as shown in FIG. 1, may be sent to TSRU(36). Tailings component (34) contains mainly water, asphaltenes,mineral matter, and small amount of solvent as well as unrecoveredbitumen. Solvent vapor and steam (together 38) are sent from TSRU (36)to a condenser (40). Water (42) and solvent are condensed in thecondenser (40) resulting in recovered solvent (44). As with recoveredsolvent (32), recovered solvent (44) may be reused in the same manner asstream (32). Tailings (47) from TSRU (36) may be further treated or maybe sent to a tailings storage area for future reclamation.

TSRU (16) and TSRU (36) will now be discussed in further detail. TSRU(16) is a flash vessel or drum maintained at an absolute pressure ofabout 100 to about 200 kPa (or about 120 to about 170 kPa, or about 140kPa). This TSRU may be operated at a temperature of about 75° C. toabout 100° C., and has internals 46. In FIG. 1, the internals (46) areillustrated as a plurality of interior, vertically spaced shed decks.Internals (46) (and internals (50) described below) may alternatively betrays, packing, baffles or other such internals known in the art. Thediluted tailings component (26) is distributed over the internals (46)to increase the surface area of the diluted tailings component (26).Below the internals (46) is a ring (not shown) having a plurality ofopenings for the release of inert gas or steam (48). The inert gas orsteam (48) counter currently contacts the downward flowing dilutedtailings component (26) distributed over the internals 46 and provideboth the necessary heat for vaporizing the solvent and a driving forcefor the vaporized solvent to the vapor phase. The internals (46) ensurethat the diluted tailings stream is spread relatively uniformly over alarge surface area that can be subsequently exposed to inert gas orsteam. A distributor (not shown), having a plurality of openings, may beused to evenly distribute diluted tailings component (26) over theinternals (46). The surface of the internals (46) may be covered with asuitable coating, such as an asphaltene fouling resistant coating, tomitigate or eliminate fouling and plugging.

An inert gas or steam (48) is introduced below the internals (46), andabove a tailings liquids pool in the bottom of TSRU (16), so that itflows counter currently diluted tailings component (26) and heatsdiluted tailings component (26) to vaporize the paraffinic solvent andsome water. The mass of inert gas or steam addition rate may varybetween 1 to 10 times the mass of the solvent depleted tailings flowfrom TSRU (16). Vaporized solvent and steam (together 27) is removedfrom the TSRU (16) as discussed above.

As the solvent depleted slurry leaves the last layer of internals (46),it is collected in a conical section of TSRU (16) to allow for pumpingfrom the bottom of TSRU (16) at a steady flow rate to either a finaldisposal area or to TSRU (36) for additional solvent recovery. Theconical arrangement creates a pool of liquid slurry. The slurry isremoved from the TSRU, as tailings component (34), using a pump in aconventional manner to the final disposal area or TSRU (36). Tailingscomponent (34) may have about the same composition of diluted tailingscomponent (26) minus the solvent recovered (32).

TSRU (36) operates in generally the same manner as TSRU (16) but ismaintained at an absolute pressure of about 20 to about 200 kPa (orabout 35 to about 125 kPa, or about 35 to about 100 kPa, or about 50kPa). The operating pressure of TSRU (36) is lower than the pressure ofTSRU (16). That is, TSRU (36) may be operated below atmosphericpressure. TSRU (36) may be operated at about 75° C. to about 100° C., orabout 82° C. to about 90° C., or about 85° C. to about 90° C., or about90° C. Because TSRU (36) may be operated at lower pressures and at belowatmospheric pressure, TSRU (36) may be operated at lower temperatures,for instance about 65° C. to about 80° C., or about 70° C. As with TSRU(16), the internals (50) of TSRU (36) are illustrated as a plurality ofinterior, vertically spaced shed decks. Inert gas or steam (52) may beintroduced below the internals (50), and above a tailings pool in thebottom of TSRU (36).

A third TSRU could also be used in series and, in each subsequent stage;the operating pressure may be lower than the previous one to achieveadditional solvent recovery. In fact, more than three TSRU's could beused.

In one embodiment, one, two, or more than two TSRU's are used where thefroth treatment tailings solvent recovery is affected in the absence of“mechanical means used to substantially break up asphaltene agglomeratesor to prevent the agglomeration of asphaltene”. The term “agglomerates”as used herein is not limited by shape and includes flocs andaggregates. The term “substantially” is used here to exclude means thatdoes not, to a substantial extent, mechanically break up asphalteneagglomerates or prevent the agglomeration of asphaltene. Non-limitingexamples of “mechanical means used to substantially break up asphalteneagglomerates or to prevent the agglomeration of asphaltene” are theagitation means described Canadian Patent No. 2,353,109 where thetailings pool is agitated to the point where the asphaltenes aredispersed, submerged and prevented from re-agglomerating and the solidsare maintained in suspension. In that patent, agitation may be effectedby a mechanical impeller, or an alternate agitation means, such as apump-around circuit to pump the slurry from the top of the liquid poolto the lower part of the liquid pool or vice versa. Another non-limitingexample of such means are the shearing conditions provided by pumps,mixers or other apparatuses, described in Canadian Patent ApplicationNo. 2,454,942, which are said to be preferably provided in the recyclecircuit first, to break up asphaltene flocs/aggregates and second, toenhance recovery of solvent from the tailings. The “mechanical meansused to substantially break up asphaltene agglomerates or to prevent theagglomeration of asphaltene” does not include means, the purpose ofwhich is unrelated to breaking up asphaltene agglomerates or topreventing agglomeration of asphaltenes, such as a pump disposed beforeor after the TSRU as shown herein.

Water may be recovered from the solvent depleted tailings stream (34 or47) downstream of the slurry pump and may be recycled for re-useupstream of the tailing solvent recovery unit in order to recovervaluable heat contained in the water, thus reducing the energyrequirements of the process. For example, recovered water may becombined with the dilution water (25) upstream of the tailings solventrecovery unit but this is not to provide additional agitation to theunit.

Example 1

In a small scale pilot test, a run was operated at about atmosphericpressure without shearing or agitation in or around TSRU (16) withinternals (46) and successfully resulted in solvent loss of less than2.8 bbl per thousand barrels of bitumen product (6). The addition ofsteam resulted in a further reduction to less than 1.0 bbl of solventloss per thousand barrels of bitumen product. A typical TSRU (16)tailings (34) sample was then subjected laboratory scale vacuumseparation tests to simulate the performance of the second stage TSRU(36). These results are shown in Table 1.

TABLE 1 Solvent Recovery Performance Pressure Average solvent SolventLoss (bbl/ (atm · abs) content (wt %) 1000 bbls of bitumen) 1.00 0.0281.18 0.79 0.024 0.97 0.59 0.015 0.63

Pumps are used to maintain a specified level in each TSRU and thevessels are sized to maintain a high downward velocity of the slurry.

As discussed herein, it has been discovered that recovery of solventfrom asphaltene agglomerates in a TSRU is effective without agitation inor around the TSRU. Thus, mechanical means used to substantiallyphysically break up asphaltene agglomerates or to prevent theagglomeration of asphaltene may be omitted. In addition to theembodiments discussed herein using internals, in another embodiment,there is provided a process for recovering paraffinic solvent from frothtreatment tailings produced in the treatment of bitumen frothcomprising: introducing the froth treatment tailings into a tailingssolvent recovery unit (TSRU) (which may or may not have internals);introducing inert gas or steam into a liquid pool formed in the bottomof the TSRU to vaporize at least a portion of the paraffinic solvent;and removing the vaporized solvent from the TSRU; wherein the frothtreatment tailings contain asphaltenes; and wherein the at least aportion of the solvent is vaporized from asphaltene agglomerates. In oneembodiment, the process is affected in the absence of mechanical meansused to substantially physically break up asphaltene agglomerates or toprevent the agglomeration of asphaltene.

The phrase “to vaporize at least a portion of the paraffinic solvent” isused herein to make clear that not all of the solvent is necessarilyvaporized. In certain embodiments, the percentage, by volume, of solventthat is vaporized is: at least 70%, at least 80%, at least 90%, at least95%, at least 98%, at least 99%, at least 99.5%, at least 99.9%, or atleast 99.9%.

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe embodiments of the invention. However, it will be apparent to oneskilled in the art that these specific details are not required in orderto practice the invention

The above-described embodiments of the invention are intended to beexamples only. Alterations, modifications and variations can be effectedto the particular embodiments by those of skill in the art withoutdeparting from the scope of the invention, which is defined solely bythe claims appended hereto.

1. A process for recovering paraffinic solvent from froth treatmenttailings produced in the treatment of bitumen froth comprising:introducing the froth treatment tailings into a tailings solventrecovery unit (TSRU), the TSRU having internals, and distributing thefroth treatment tailings over the internals to increase the surface areaof the froth treatment tailings; introducing inert gas or steam belowthe internals so that it flows counter currently to the froth treatmenttailings and heats the froth treatment tailings to vaporize at least aportion of the paraffinic solvent; and removing the vaporized solventfrom the TSRU; wherein: the froth treatment tailings containasphaltenes; and the at least a portion of the solvent is vaporized fromasphaltene agglomerates.
 2. The process of claim 1, wherein the processis affected in the absence of mechanical means used to substantiallybreak up asphaltene agglomerates or to prevent the agglomeration ofasphaltene.
 3. The process of claim 1, wherein the TSRU has an absolutepressure of about 100 and about 200 kPa.
 4. The process of claim 1,wherein the internals comprise a plurality of interior, verticallyspaced shed decks.
 5. The process of claim 1, wherein the internals arecoated with an asphaltene fouling resistant coating to mitigate foulingor plugging in the TSRU.
 6. The process of claim 1, wherein the frothtreatment tailings contain at least 1.0 wt % asphaltenes.
 7. The processof claim 1, wherein the froth treatment tailings contain at least 5.0 wt% asphaltenes.
 8. The process of claim 1, wherein the inert gas or steamintroduced below the internals is introduced above a liquid level thatforms in the bottom of the TSRU.
 9. The process of claim 1, wherein theparaffinic solvent is a C₄ to C₆ paraffinic hydrocarbon solvent.
 10. Theprocess of claim 1, wherein the paraffinic solvent is pentane,iso-pentane, or a combination thereof.
 11. The process of claim 1,wherein the temperature of the TSRU is about 75 to about 100° C.
 12. Theprocess of claim 1, wherein the TSRU has an absolute pressure of about120 to about 170 kPa.
 13. The process of claim 1, wherein the inert gasis nitrogen, methane, carbon dioxide, argon, steam or any other inertgas that is not reactive under process conditions.
 14. The process ofclaim 1, wherein the inert gas or steam to froth treatment tailings massratio is about 1:1 to about 10:1.
 15. The process of claim 1, furthercomprising feeding tailings from the TSRU into a second TSRU maintainedat an absolute pressure that is lower than the pressure of the TSRUrecited in claim 1, the second TSRU having internals, and distributingthe tailings from the TSRU over the internals to increase the surfacearea of the tailings from the TSRU; introducing inert gas or steam belowthe internals of the second TSRU so that it flows counter currently tothe tailings from the TSRU and heats the tailings from the TSRU tovaporize at least a portion of the paraffinic solvent; and removing thevaporized solvent from the second TSRU.
 16. The process of claim 15,wherein the second TSRU has an absolute pressure of about 20 to about200 kPa.
 17. A process for recovering paraffinic solvent from frothtreatment tailings produced in the treatment of bitumen frothcomprising: introducing the froth treatment tailings into a firsttailings solvent recovery unit (TSRU), the first TSRU having internals;distributing the froth treatment tailings over the internals to increasethe surface area of the froth treatment tailings; introducing inert gasor steam below the internals so that it flows counter currently to thefroth treatment tailings and heats the froth treatment tailings tovaporize at least a portion of the paraffinic solvent; removing thevaporized solvent from the first TSRU; feeding tailings from the firstTSRU into a second TSRU maintained at an absolute pressure that is lowerthan the pressure of the first TSRU, the second TSRU having internals;distributing the tailings from the first TSRU over the internals of thesecond TSRU to increase the surface area of the tailings from the firstTSRU; introducing inert gas or steam below the internals of the secondTSRU so that it flows counter currently to the tailings from the firstTSRU and heats the tailings from the first TSRU to vaporize at least aportion of the paraffinic solvent; and removing the vaporized solventfrom the second TSRU.
 18. The process of any one of claims 22 to 25,wherein the froth treatment tailings contain asphaltenes; wherein the atleast a portion of the solvent is vaporized from asphalteneagglomerates; and wherein the process is effected in the absence ofmechanical means used to substantially break up asphaltene agglomeratesor to prevent the agglomeration of asphaltene.
 19. A process forrecovering paraffinic solvent from froth treatment tailings produced inthe treatment of bitumen froth comprising: introducing the frothtreatment tailings into a tailings solvent recovery unit (TSRU);introducing inert gas or steam into a liquid pool formed in the bottomof the TSRU to vaporize at least a portion of the paraffinic solvent;and removing the vaporized solvent from the TSRU; wherein: the frothtreatment tailings contain asphaltenes; and the at least a portion ofthe solvent is vaporized from asphaltene agglomerates.
 20. The processof claim 19, wherein the TSRU is substantially free of internals. 21.The process of claim 19, wherein the process is effected in the absenceof mechanical means used to substantially break up asphalteneagglomerates or to prevent the agglomeration of asphaltene.
 22. Theprocess of claim 19, wherein the froth treatment tailings contain atleast 1.0 wt % asphaltenes.
 23. The process of claim 19, wherein thefroth treatment tailings contain at least 5.0 wt % asphaltenes.
 24. Theprocess of claim 19, wherein the TSRU has an absolute pressure of about20 and about 200 kPa.
 25. The process of claim 19, wherein theparaffinic solvent is a C₄ to C₆ paraffinic hydrocarbon solvent.
 26. Theprocess of claim 19, wherein the paraffinic solvent is pentane,iso-pentane, or a combination thereof.
 27. The process of claim 19,wherein the temperature of the TSRU is about 75 to about 100° C.
 28. Theprocess of claim 19, further comprising feeding tailings from the TSRUinto a second TSRU maintained at an absolute pressure that is lower thanthe pressure of the TSRU recited in claim 19.